IGCSE Biology Paper-4: Specimen Questions with Answers 141 - 142 of 279

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Passage

Cotton, Gossypium hirsutum, is grown for the fibers that form within the fruits after fertilization, as shown in Fig.

Fibers from the fruits of cotton plants are used in the textile industry.

The Fibres
  • Cotton plants have been genetically engineered to produce a protein that is toxic to the caterpillars of several insect pests. This gives the cotton plants resistance to the pests.
  • The cry gene for pest resistance was isolated from the bacterium Bacillus thuringiensis and inserted into the cells of cotton plants as shown in Fig.
Bacterial DNA

Question 141 (4 of 5 Based on Passage)

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Short Answer▾

Outline the advantages to farmers of growing genetically engineered cotton plants that contain the toxic protein.

Explanation

  • It improves production and raise farmer՚s income. Farmers are still practicing traditional process of seeding and cultivation, which required scientific moves for raising their production. Hence, it is one of the moves to enhance the farm production.
  • It reduces the use of pesticide and insecticide during farming that might be great moves for the betterment of the food supply.
  • It can feed a rapidly increasing population because it shows dramatically increased yields.
  • It can produce more in small area of land.
  • BT cotton greatly reduced the use of toxic pesticides. BT cotton produces a common soil bacterium, Bacillus thuringiensis (BT) . It is a natural pest repelling bacterium that is toxic to many worms and pests that can harm the crop but is not hazardous to humans. BT is widely sprayed on crops by organic farmers as a pesticide.

Question 142 (5 of 5 Based on Passage)

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Short Answer▾

An enzyme cuts the cry gene from the DNA of B. thuringiensis.

State the name of the regions labelled A on Fig.

Explanation

Restriction enzymes cut the strand of DNA a little away from the center of the palindrome sites but between the same two bases of the opposite strands. This leaves single stranded unpaired bases at cut ends. These ends with unpaired bases are called sticky ends or cohesive ends. The latter are named so because they form hydrogen bonds with their complementary cut counter parts. The sticky ends facilitate the action of the enzyme DNA ligase.

Endonuclease and Sticky Ends

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